Personally, I look at the current rate of technological advancement, and I think the sky's the limit.

My imagination tends towards solving the main problems of human spaceflight, with the development of custom-designed artificial bodies better suited to the radiation and zero/micro-gravity space environment; and the construction of space habitats both orbital and mobile by private hobbyists' clubs.

The stuff we do late in this century, assumiming prosparity continues, depends on break thoughs we make the next decade or two. Will we mass produce CNT = carbon nano tubes or something even stronger? Will we mass produce room temperature super conductors? Will we have practical space elevators, fusion, SSP = space solar power? Gigawatt (average power) lasers?
If the world ecconomy is bad the last half of this century we may make little progress after 2050. Neil

Duh. Thats why they invented World of Warcraft, to keep geeks distracted.

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"I worry that, especially as the Millennium edges nearer, pseudo-science and superstition will seem year by year more tempting, the siren song of unreason more sonorous and attractive." - Carl Sagan, 1995

But we are talking now and we know the truth! This is how the revolution begins!

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Rovers forever! - ToSeek
"Carl Sagan sent a message to ET,
Neil Armstrong walked in the Sea of Tranquility
Steve Squyers built Spirit and Opportunity
Dan Haylen upchucked in zero gravity." -Brent Simon, The Space Camp Song
'Evolution and science are one thing, but you don’t mess with Yoko Ono. Everybody knows that. ' - 386sx

If we could design artificial bodies, who needs habitats? We could live anywhere, including deep space. But it may not even be possible to do so, and if it is, I doubt it'll happen this century. Or next, for that matter. But the problems of zero-g and radiation are solveable using existing technology-- spinning, well-shielded spacecraft. It's not so much a matter of technology as of priority and effort; the materials just need to be put where they're needed.

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"If this were play'd upon a stage now, I could condemn it as an improbable fiction."
Shakespeare, Twelfth Night
Illuminati's Razor-The most complicatedly evil answer is usually the most correct answer. - Fazor
"Every book is a children's book if the kid can read." - Mitch Hedberg
"Distance doesn’t matter much in space, where if you just start a thing off with the right kind of shove, sooner or later it will get where you want it to go." -Frederik Pohl, Mining the Oort

I guess intelligent or semi-intelligent autonomous probes will have gone most everywhere significant in-system. They could be exploring the Oort cloud by moving from asteroid to asteroid, using either ice or other common material to refuel their drives and possibly using local raw materials in nano-factories to repair themselves.

Without general purpose nano-factories (or similar) I don't see much (if any) of a human presence off-Earth. Though I guess we will learn a lot about terraforming from the geo-engineering projects we undertake to tackle global warming.

I suspect we will have a deliberately captured asteroid or three in Earth orbit by 2100 (one per major space power?). Which we use as habitat and as manufacturing platforms for space probes and orbital assets, probably including an interstellar program.

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Always challenge the assumptions

Why? What about just using the exisiting plans for space-adapted manufacturing methods and biological-based life support? These ideas have been and continue to be developed using only existing and easily reached near-term technology. Space colonization doesn't need Wondertech to become a practical reality. It's perfectly feasible using only simple engineering and application of known methods.

Why not just use them where they are? Dragging them to Earth orbit will be more difficult-- and far more dangerous-- than sending a manned manufacturing platform to a convenient NEO.

__________________
"If this were play'd upon a stage now, I could condemn it as an improbable fiction."
Shakespeare, Twelfth Night
Illuminati's Razor-The most complicatedly evil answer is usually the most correct answer. - Fazor
"Every book is a children's book if the kid can read." - Mitch Hedberg
"Distance doesn’t matter much in space, where if you just start a thing off with the right kind of shove, sooner or later it will get where you want it to go." -Frederik Pohl, Mining the Oort

Another big unknown here: what exactly will a human and a robot look like at the end of this century - the difference between the two might become blurry.

Actually, I would be surprised to find 'nations' still dominate space exploration by 2100.
Private enterprise should be the key factor by then.

Highly unlikely. The inherent short-sighted nature of private enterprise makes it poorly suited to space exploration. The current lack of anything worthwhile from the private sector (even given all the public resources they've been handed) bears this out. The whole 'space enterprise' thing is just a silly dream of entrepreneurs and free market ideologues.

__________________
"I worry that, especially as the Millennium edges nearer, pseudo-science and superstition will seem year by year more tempting, the siren song of unreason more sonorous and attractive." - Carl Sagan, 1995

I am rubber, you are glue...
(Common schoolyard response to insults in my primary school days)

__________________
Rovers forever! - ToSeek
"Carl Sagan sent a message to ET,
Neil Armstrong walked in the Sea of Tranquility
Steve Squyers built Spirit and Opportunity
Dan Haylen upchucked in zero gravity." -Brent Simon, The Space Camp Song
'Evolution and science are one thing, but you don’t mess with Yoko Ono. Everybody knows that. ' - 386sx

Which is exactly why I'm betting on privately-funded space enthusiast clubs, many of whose members are funding their spacefaring dreams by getting rich in long-proven terrestrial private eneterprises.

Silly or not, they look like beating all state-funded ventures to the moon this time:
http://www.googlelunarxprize.org/

Quite a bit less expensive, too

And don't you like rooting for the little guy, Damburger?

__________________
Rovers forever! - ToSeek
"Carl Sagan sent a message to ET,
Neil Armstrong walked in the Sea of Tranquility
Steve Squyers built Spirit and Opportunity
Dan Haylen upchucked in zero gravity." -Brent Simon, The Space Camp Song
'Evolution and science are one thing, but you don’t mess with Yoko Ono. Everybody knows that. ' - 386sx

Has yet to produce on iota of, well, anything. Even if it does result in a lunar launch it doesn't necessarily follow that it will lead to anything.

I don't consider millionaires and billionaires playing astronaut to be the 'little guy'. You can't possibly believe that the massively rich sending themselves and their peers into space will somehow translate into anything that will benefit the population at large.

__________________
"I worry that, especially as the Millennium edges nearer, pseudo-science and superstition will seem year by year more tempting, the siren song of unreason more sonorous and attractive." - Carl Sagan, 1995

Well, it'll create jobs...jobs that will pay less and less (when factoring inflation) every year.

Trickle-down economics? Are you kidding me?

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"I worry that, especially as the Millennium edges nearer, pseudo-science and superstition will seem year by year more tempting, the siren song of unreason more sonorous and attractive." - Carl Sagan, 1995

But certainly the governments are the 'big guys'.

__________________
Rovers forever! - ToSeek
"Carl Sagan sent a message to ET,
Neil Armstrong walked in the Sea of Tranquility
Steve Squyers built Spirit and Opportunity
Dan Haylen upchucked in zero gravity." -Brent Simon, The Space Camp Song
'Evolution and science are one thing, but you don’t mess with Yoko Ono. Everybody knows that. ' - 386sx

Yes, having lived through the years since we were blessed with Reaganomics, I feel I have been trickled on quite enough, thank you.